Damage reduction

Damage Reduction

Damage reduction in percent for melee attacks taken from a target of the same level. Note that this graph peaks at 75% for all levels, since this is the maximum damage reduction gain from armor.

Armor reduces physical damage done against you by a certain proportion. It depends entirely on the level of the monster (or player) hitting you and your own armor. Your level doesn't matter. By hovering your mouse over Armor on your Character screen, you can see the percentage value of this reduction for damage done by enemies that are at your current level. This percent reduction will actually fall as soon as you gain a level if you're still wearing the same armor. You haven't lost anything, it's merely showing you that your armor isn't as effective against monsters one level higher than you used to be.

The most important thing to remember about armor is:

An X% increase in armor means an X% increase in armor's contribution to the amount of damage you can take.

The formula for the base armor value is

Base Armor = 2 * Agility + gear armor + magic armor

Gear armor is the armor value from the gear you are wearing. Magic armor is the extra armor from buffs such as scrolls, mage armor, armor kits etc.

Note that talents which give a percentage bonus to armor (like druid bear form) do not include magic armor in their boost to the armor rating. This is especially important for druids since bonuses received from armor kits, sets and green effects in general are not affected by bear form and Thick Hide.

For enemies from level 1 to 59, the reduction to physical damage, as a percentage, is given by the following formula

%Reduction = (Armor / (Armor + 400 + 85 * Enemy_Level)) * 100

For enemies from level 60 and up, the reduction to physical damage, as a percentage, is given by the following formula

%Reduction = (Armor / (Armor - 22167.5 + 467.5 * Enemy_Level)) * 100

For level 70 enemies and raid bosses, this simplifies to

%Reduction vs. 70 = (Armor / (Armor + 10557.5)) * 100

%Reduction vs. 73 = (Armor / (Armor + 11960)) * 100

Note that the maximum damage reduction is capped at 75%.

Damage Soak

Although the character sheet tooltip gives the amount of damage that the armor absorbs, it is more useful to think of how much more damage the player can take.

In general, the armor reduction formula can be written as

Reduction = Armor / (Armor + X)

If the enemy is lower than level 60, X = 85 * Enemy_Level + 400

If the enemy is level 60 or higher, X = 467.5 * Enemy_Level - 22167.5

Therefore, the amount of damage that the player takes after their armor's damage reduction is applied is

Damage_Taken = Damage_Dealt * ( 1 - ( Armor / (Armor + X) ) )

or

Damage_Taken = Damage_Dealt * ( X / (Armor + X) )

So the ratio of damage dealt to damage taken is

Damage_Dealt / Damage_Taken

or

(Armor + X) / X

or

1 + (Armor / X)

Therefore, the increase in the amount of damage the player can take compared to having no armor at all, as a percentage, is

(Armor / X) * 100

Therefore, an X increase in armor (compared to 0 armor) means an 100% increase in the amount of damage the player can take.

e.g. For a level 70 enemy, X = 10557.5. So a player with 10557.5 armor attacking a level 70 enemy would be able to take 100% more damage. A player with 31672.5 armor would be able to take 300% more damage than a player with 0 armor (which is the maximum).

Armor required to get X% damage reduction

To calculate the amount of armor needed for maximum mitigation against a lvl 59 or below enemy, one can use the following formula:

Armor = 1200 + 255 * Enemy_Level

Thus a lvl 59 character who wants to achieve 75% reduction vs. lvl 59 mobs would need 16245 AC. Note that this changes beyond lvl 59, as the formula to calculate damage reduction for levels 60 and up requires much more armor to get the same mitigation; in particular, it's impossible with the current itemization for any level 70 character to get permanently the maximum damage mitigation from armor of 75% against enemies lvl 70-73. But well geared Druids in Bear form under effect of  [Legacy of the Mountain King] can temporarily have 75% mitigation against lvl 70 mobs. (This is incorrect, it is possible to achieve these armor numbers unbuffed with current items - 8/2/07 (see this page))

Or a more general formula. The amount of armor needed for a specific reduction is:

Armor = %Reduction * (400 + 85 * Enemy_Level) / (100 - %Reduction)

Against a level 59 and less

Armor = (400 + 85 * Enemy Level ) / ( 100 / %Reduction - 1)

Against a level 60 and up

Armor = (467.5 * Enemy Level - 22167.5 ) / ( 100 / %Reduction - 1)

Armor required to get 50%, 60%, 70% and 75% damage reduction against lvl 60, 63, 70 and 73 mobs.

	Damage reduction
Enemy lvl	50%	60%	70%	75%
60	5883	8824	13725	17648
63	7285	10928	16999	21855
70	10558	15837	24635	31673
73	11960	17940	27907	35880